This invention relates to a method for cleaning samples of compounds containing inorganic or organic materials during producing processes of electronic materials, magnetic materials, optical materials, ceramics, etc., and a process for producing products such as semiconductor devices using the cleaning method. Particularly, this invention relates to a cleaning method suitable for preventing or remarkably reducing adhesion of fine particles on semiconductor substrate surfaces and a process for producing a semiconductor device using said cleaning method.
Integrated circuit formed on a surface of a substrate such as a semiconductor wafer, etc. has recently been increased in level of integration, and thus the line width of pattern becomes finer and finer. In the next stage 64 M DRAMs, the minimum fabrication size is 0.3 .mu.m and finer particles will become a bar for improving the quality and yield of products in their production processes.
Heretofore, as a means for cleaning a substrate surface, there is a method in which a mixed solution of ammonia water and hydrogen peroxide solution is heated to about 80.degree. C. and a wafer is immersed therein, or a method in which a wafer is subjected to ultrasonic wave treatment in ultrapure water, as disclosed in RCA Review, 31 (1970), pp. 187-206.
Further, there is also a method wherein SiO.sub.2 film 39 (shown in FIG. 16) is removed by wet etching without removing a resist 37. According to this method, as shown in FIG. 16, a SiO.sub.2 film 39 and a poly Si film 40 are formed on a poly Si film 38, and used for forming a fin structure. Then, the resist 37 and SiO.sub.2 film 39 are removed, followed by formation of Si.sub.3 N.sub.4 (not shown in FIG. 16) on the poly Si 38 and 40 to give 1.5 fins structure.
Considering higher density of the level of integration in the integrated circuit and the minimum fabrication size of 0.3 .mu.m in the next stage 64 M DRAMs, the size of fine particles to be cleaned becomes smaller and small, and it will be necessary to remove even fine particles having a size of 0.03 .mu.m.
With a reduction of the size of fine particles, the amount of fine particles in the air also increases. Thus, the amount of fine particles of 0.03 .mu.m will be present several times as large as that of fine particles of 0.05 .mu.m now produced (16 M DRAMs). Further, with the reduction of size of fine particles, these fine particles will more easily adhere to a substrate, resulting in requiring cleaning technique for the fine particles more often.
But, according to a prior art technique for removing fine particles from a substrate using mechanical force such as ultrasonic wave, since the mass and surface area are also reduced with a reduction of size of fine particles, the chargeable mechanical force per particle decreases and thus it becomes difficult to remove the fine particles. Further, damages on substrates also become a problem with an increase of level of integration of semiconductors. Thus, it will be impossible to remove very finer particles according to the prior art techniques.
For example, the use of a mixed aqueous solution of hydrofluoric acid and ammonium fluoride is considered. Fine particles present in such a mixed aqueous solution seem to be derived from those generated by various factors such as removal of fine particles attached to a rear side of a semiconductor wafer, and those generated newly by etching of an oxide film. Particularly in the latter case, the fine particles include those having Si as a major component and generated by chemical reactions, and the like at the time of etching of the oxide film, those of reaction products attached to the substrate prior to the etching such as dry etching of the oxide film and released by etching. It is very difficult to prevent such fine particles generated by the latter case from adhesion to the substrate, even if the above-mentioned mixed aqueous solution and the rear side of semiconductor wafer are made clean.
Further, in the case of 1.5 fins structure mentioned above, since the poly Si film surface 38 (see FIG. 16) is exposed after wet etching of the SiO.sub.2 film 39, fine particles are adhered to the poly Si film surface 38. More concretely, fine particles were adhered to the product in an amount of 0.9 particle/cm.sup.2 or more.
Such fine particles adhered to the wafer become one of major factors for reducing the yield of products in the production of semiconductor devices.